One or more single light emitting diodes (LEDs) are provided as the light sources in previously known reading lamps and spotlights. These LEDs are either a monochromatic white with a fixed white color, or consist of several individual LEDs in various colors, wherein the colors of individual LEDs are mixed, in particular for generating white light. In addition, isolated use is already being made of multi-chip LEDs for RGB spotlights (red-green-blue lamps).
As evident from FIG. 1, known reading lamps and spotlights focus the light generated by a light source, e.g., an LED S, onto a surface to be illuminated, for example onto reading plane B, by means of an optical system consisting of a collective lens with focal distance f1 as the primary lens L1, an aperture G and a collective lens with a focal distance f2 as the secondary lens. The aperture G is arranged between optics (lenses) L1 and L2 in a variable distance d from the primary optics (lens) L1, wherein the distance d can correspond to the focal distance f1. The object distance between the aperture G and secondary lens L2 is marked g, while the image distance b is located between the secondary lens L2 and the surface to be illuminated/reading plane B. Since the image distance b is generally very large (to infinity) by comparison to the object distance g, the object distance g roughly corresponds to the focal distance f2 of the secondary lens L2. The LED S is arranged at the input-side focal point f1 of the primary lens L1, so that a parallel light bundle exits the primary lens L1, passes through the aperture G, and is deflected by the secondary lens L2 onto the surface to be illuminated/reading plane B, preferably bundled. A two-stage lens system is also often used for improved illumination of the aperture G, wherein the job of the first lens is mainly to collect the light from the light source, while the second lens directs this light specifically toward the aperture G. Such an optical system along with the system shown on FIG. 1 always requires at least the length of two focal distances (twofold focal distance length) in the radiating direction, specifically roughly one focal distance f1 of the primary lens L1 and one focal distance f2 of the secondary lens L2, in addition to the distance d between the primary lens L1 and aperture G. The disadvantage here is that the structural volume of the lamp, in particular the depth, must measure a specific minimum value.
DE 103 07 147 A1 describes a reading lamp for aircraft cabins that can be installed via a passenger seat in particular. A small halogen or LED lamp is preferably provided as the light source. The reading lamp is compact with a small installation volume, and makes it possible to adjust the lamp in a relatively broad range. It is a projecting reading lamp with horizontal optical axis, wherein the emitted light rays are diverted by an optical deflection means in the sitting area of the allocated passenger seat. This reading lamp also has an optical lens system, which consists of a focusing lens, an aperture and a converging lens, so that the structural volume of the lamp must here also measure a minimum value established by these components. The structural depth is decreased by shifting the optical path from the vertical to the horizontal axis.
Known from DE 10 2006 047 941 A1 is a device for homogenizing the emission of rays, in particular of light with irregular micro-lens arrays, wherein at least one lens arrangement has a plurality of lens systems arranged with parallel optical axes. The lens systems are at least partially not identical, wherein not identical means that the parameters for the array lenses, e.g., the bending radius, the free diameter, the vertex position or others, can vary form one lens to the next. However, the not identical lens system always has the same numerical aperture in a first direction parallel to the main plane of the lens system.
DE 10 2004 004 778 A1 describes a light-emitting diode lighting module with one or more light-emitting diode components and an optical device for beam shaping, which are placed downstream from the light-emitting diode component(s). The optical device has a beam-bundling optical element for each light-emitting diode component, and a beam-expanding optical element situated downstream from it as viewed from the light-emitting diode component. A light-emitting diode component that emits a red light, green light and blue light can be respectively provided, wherein the beam-expanding optical element mixes the light from the three light-emitting diode components.
Known from DE 10 2005 028 671 A1 is a method for controlling the color components of a lighting device for micro-display projection systems with several color light sources, for example LEDs or OLEDs. The light sources are controlled independently of each other. Provided to generate the color image are time windows, in which color sequential partial color images are generated, for example, for red, green or blue. The initial values for the target window components of the color light sources are empirically determined to ascertain a white point in the CIE color triangle lying in proximity to the target white light point. A combination of sequentially additive color mixing and color mixing according to the superposition principle is performed, resulting in a relative adjustment of the lighting device to the system-dependent color area or spectral transmission properties of the projection system. To control the color components, FIG. 1 of this publication depicts a CIE color triangle with a representation of the light source color locations and target color locations. The CIE color triangle integrates a color triangle comprised of the light source color locations for the primary colors green, red and blue, which also incorporates another penciled-in color triangle formed by the target color locations of the primary colors. After determining the position (coordinates) of the light source color locations and the power ratios of the color light sources in each time window, the light source color locations are transformed into the desired target color locations, wherein another white point lying in proximity to the target white point is formed. The disadvantage to this projection arrangement is that only enables the achievement of a relatively small CRI color rendering index, wherein the colors are mixed by chronologically actuating the individual primary colors green, red and blue.
Evident from DE 10 2005 061 204 A1 is a lighting device that encompasses at least one LED of a first color, preferably blue, at least one LED with a second color, preferably red, and preferably an LED of a third color, preferably green, as well as at least one white LED, all arranged on a shared substrate. A lighting controller for the lighting device encompasses among other things various controllable power sources for LEDs of different color for generating independently controlled operating signals for the LEDs of different color. The white LED can consist of a blue or UV-LED and a light converter allocated thereto. The lighting device can also encompass two or more LEDs of the same color, including white. The LEDs can be selected based on factors like wavelength and intensity, wherein such a device can cover more than 85% of the visible color space when using this distribution along with two green LEDs. FIG. 10 of this publication shows a graphic depiction of the color coordinates in the color space of the lighting device described above, wherein an outer elliptical shape represents all visible wavelengths, while an outer elliptical shape represents the colors that can be generated. A curved line in the middle of the triangular shape is referred to as a white line, since this line represents all combinations of the LEDs at all the different color temperatures that generate white light in a combination. A high CRI color rendering index is also not achieved in this lighting device.